Method and apparatus for nitrogen oxide emission of a direct injection

Abstract

Direct-injected engines often operate in broad characteristic field areas with stratified charging, with the harmful emissions not being sufficiently reducible by exhaust recirculation means. Nitrogen oxide molecules are not selectively catalytically reducible In oxygen-rich exhaust during stratified combustion; thus a storage catalytic converter is often located in the exhaust stream to adsorb the resultant nitrogen oxide molecules. In order to initiate desorption and reduction of stored nitrogen oxide molecules, a stoichiometric exhaust composition must be created for a certain operating interval. It was previously assumed that stoichiometric air ratios can only be attained with homogeneous carburetion, so that a switch is made to injection on the intake stroke from fuel injection on the compression stroke. In order to produce a method for reducing nitrogen oxide emissions from a direct-injected gasoline engine, which reduces nitrogen molecules during continuous stratified charging, provision is made to increase the exhaust gas circulation rate for the required operating interval, depending on the operating point of the engine, by a certain amount to create a stoichiometric exhaust composition before the adsorption capacity limit of the storage catalytic converter is reached.